The present invention generally relates to a storage system having a RAID group.
In technology called RAID (Redundant Array of Independent (or Inexpensive) Disks), a RAID group, which stores data in an arbitrary RAID level (for example, RAID 5, RAID 6), is constructed. The RAID group is constituted from an arbitrary number of physical storage devices.
Technology for changing a RAID level is known. This type of technology, for example, is disclosed in Japanese Patent Laid-open No. 2006-318017. According to Japanese Patent Laid-open No. 2006-318017, an array group (equivalent to a RAID group), which is made up of an arbitrary number of disks, is divided into a plurality of redundancy groups. At least one redundancy group in each array group is treated as an unused redundancy group. When the RAID type (equivalent to a RAID level) is changed in one array group, the RAID type is changed for each redundancy group related to the change-targeted RAID type by moving the data stored in a redundancy group to the unused redundancy group, and changing the source redundancy group to the unused redundancy group.
According to Literature 1, the respective redundancy groups constituting a RAID group span all the disks, and at least one of the plurality of redundancy groups is treated as an unused redundancy group. Thus, even if an error is likely to occur on a certain disk in the RAID group, this error-susceptible disk can be made the data destination for a RAID level change.